1. Field of the Invention
The present invention relates to an image pickup apparatus including a solid-state image pickup device, such as a complementary metal oxide semiconductor (CMOS) imager, and to a method of correcting image data captured by the image pickup apparatus.
2. Description of the Related Art
In recent years, there is an increasing need for solid-state image pickup devices, such as charge coupled device (CCD) imagers and CMOS imagers, used in video cameras and digital still cameras to increase the number of pixels and to reduce in size. The increase in the number of pixels along with the reduction in size causes the area per pixel to be decreased, thus possibly lowering the pixel sensitivity.
In order to resolve such a problem, the proportion of photodiodes in the pixel structure of the solid-state image pickup devices, which includes the photodiodes and a peripheral circuit including amplifier transistors and reset transistors, has been increased as much as possible by devising the circuitry and the wiring layout and/or developing the manufacturing processes to achieve both the increase in the number of pixels and the reduction in size.
However, the recent demand for the solid-state image pickup devices to increase the number of pixels and to reduce in size is increasing and, at the same time, an improvement in the image quality at lower illumination draws attention. Accordingly, it may not be possible to provide the solid-state image pickup devices capable of achieving the pixel sensitivity that ensures a desirable image quality only by the above action.
In these situations, pixel sharing technologies receive widespread attention in order to overcome the above drawback of the solid-state image pickup devices. In the pixel sharing technologies, part of the circuits necessary for the pixel structure, for example, the amplified transistors and/or the reset transistors, are shared between multiple pixels that are horizontally and/or vertically adjacent or near to each other to reduce the circuit area (including the wiring) of each pixel and to increase the proportion of the photodiode by the amount corresponding to the reduction in the area, thereby improving the pixel sensitivity.
For example, Japanese Patent Application No. 3838665 discloses a pixel sharing technology of sharing the amplified transistor and the reset transistor necessary to read out pixel data from each pixel between two adjacent pixels. In this technology, the pixel data is read out from each pixel while the two adjacent pixels connected to the amplified transistor and the reset transistor are sequentially selected at slightly different times to decrease the number of transistors per pixel and to increase the area for the photodiodes by the amount corresponding to the decrease in the number of transistors in order to improve the pixel sensitivity.
In general solid-state image pickup devices that do not adopt the pixel sharing technology, all the pixels are normally configured uniformly. In other words, the pixel structure of the general solid-state image pickup devices is always common to the pixels at any positions on the screen. Accordingly, the photodiodes of all the pixels have the same peripheral environment in the semiconductor structure in such general solid-state image pickup devices. Consequently, the optical characteristics are basically common to all the pixels if the factor of a variation in the manufacturing is excluded.
However, in the solid-state image pickup devices to which the “pixel sharing technology” is applied and which is disclosed in, for example, Japanese Patent Application No. 3838665, all the pixels have the same structure when the multiple pixels that share the circuit and that are adjacent or near to each other are considered as one unit. However, the pixels arranged at different positions in the unit have different peripheral environments in the semiconductor structure. Accordingly, in the solid-state image pickup devices adopting the pixel sharing technology, the arrangement pattern of the multiple pixels sharing the circuit is repeated to form the circuit layout.
Specifically, when the multiple pixels sharing the circuit are considered as one unit, the multiple units are repetitively arranged horizontally and vertically in the solid-state image pickup devices. Since the photodiodes of the pixels arranged at the same position in the arrangement patterns of the pixels in the multiple units have the same peripheral environment in the semiconductor structure, the pixels have the same optical characteristics.
However, since the pixels arranged at different positions in the arrangement patterns of the multiple pixels sharing the circuit, that is, the pixels that are adjacent or near to each other in the units have different circuitries and/or layouts, the photodiodes of the pixels have different peripheral environments in the semiconductor structure, thus providing different pixel characteristics.
Accordingly, even if images of fully uniform subjects are captured with the solid-state image pickup devices to which the “pixel sharing technology” is applied, different values are output from the adjacent pixels in one unit and, therefore, there is a problem in that the quality of the finally output images may be greatly dropped.
In related art, in order to avoid the above problems involved in the pixel sharing, technologies of devising the pixel structure of the solid-state image pickup devices are disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2004-172950, Japanese Unexamined Patent Application Publication No. 2005-110104, Japanese Unexamined Patent Application Publication No. 2005-73733, and Japanese Unexamined Patent Application Publication No. 2006-157953. In such technologies, for example, (A) the pixel layout is devised to reduce the optical nonuniformity as much as possible or (B) the pixel sharing is performed so as not to adversely affect the output images even if the optical nonuniformity occurs.